B757 Flight Crew encounters light to moderate turbulence at FL390 and requests FL370. Turbulence is worse lower and further descent is requested which is slow in coming. This results in an emergency declaration and descent to FL310 to avoid severe turbulence.
Synopsis
B757 Flight Crew encounters light to moderate turbulence at FL390 and requests FL370. Turbulence is worse lower and further descent is requested which is slow in coming. This results in an emergency declaration and descent to FL310 to avoid severe turbulence.
Narrative
Enroute at FL390 seat belt sign was on with continuous LT(Light)-MOD(Moderate) chop. Requested altitude change. Cleared to FL370. Ride rapidly transitioned to MOD-SVR(Severe) turbulence. ATC advised and we requested immediate further descent to FL270. ATC said something about us to expect lower in xx minutes. Ride continued to deteriorate to severe turbulence; ATC advised; and we requested turn for descent. We were cleared to descend 1000 feet. We did and requested further descent. I noted 160+ Kt Wind on the tail. F/O again requested descent and advised ATC of ride conditions; again given 1000 foot descent. I could not see other aircraft painting on TCAS below. We declared an emergency and advised ATC of our further descent. We were then cleared to FL270. Ride transitioned from severe turbulence out of FL320. Removing the aircraft from severe turbulence was our primary effort. This process required F/O's 100% attention. This primary duty precluded other things such as cabin announcement; as the Seat Belt sign was fortunately already ON. My impression was that ATC treated our transmissions as routine; and too much and time effort was spent requesting altitude change after reporting severe turbulence. We never did get clearance. We declared an emergency and stated intentions. After level off I determined there were no injuries; no apparent aircraft damage; briefed passengers via PA and reported to Dispatch and Maintenance. After level off in our sector; and after hand off to another sector; we were never queried with usual post emergency declaration questions; such as if assist needed; number of souls; if were still emergency status; etc. I do not know if ATC was unresponsive to our declaration in other unobserved areas.
Second reporter narrative
Encountered unreported moderate turbulence at FL390. Requested descent. Immediately encountered severe turbulence. ATC was unhelpful/refused timely descent. Declared emergency and initiated descent while in severe turbulence. Turbulence ended very abruptly at FL310. Wind change was 100 knots in less than 5000 ft. No injuries.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.